In order to improve a cycle efficiency of a two-stage or multi-stage centrifugal compressor, a cycle with an economizer is often used. A flashing gas refrigerant in the economizer enters into a next-stage impeller or a bend of a return device via a gas-supplementing passage for supplementing gas. A gas-supplementing mode may be single-point gas supplement, or 360° annular gas supplement. The single-point gas supplement may generate local turbulence losses, thereby resulting in a certain efficiency waste, and limiting a usage range. The 360° annular gas supplement may be better integrated with a previous-stage impeller, so that gas is more uniform, and turbulence losses are reduced to the greatest extent, thereby better improving cycle efficiency.
A gas-supplementing position of a 360° annular gas-supplementing structure is not specially treated, generally. Once a flowing speed of gas at the gas-supplementing position is high or low relative to that of gas in a diffuser passage, turbulence losses will be generated, thereby affecting the cycle efficiency of the entire compressor.
In view of the above problems, it is urgently necessary to provide a novel centrifugal compressor gas-supplementing structure, so as to solve a problem in the prior art of influence on the cycle efficiency of an entire compressor caused by turbulence losses due to mixing of supplemented gas and gas in a gas passage of the compressor.